1. Field of the Invention
Ion cyclotron resonance (ICR) is a known phenomena and has been employed in the context of mass spectroscopy. Essentially, this mass spectrometer technique has involved the formation of ions and their confinement within a cell for excitation. Ion excitation may then be detected for spectral evaluation.
With the advent of Fourier Transform mass spectroscopy, rapid and accurate mass spectroscopy became possible. This technique is disclosed in U.S. Pat. No. 3,937,955 issued Feb. 10, 1976 to Comisarow and Marshall, which is commonly owned with the present invention and which is hereby incorporated by reference. While this technique provided a vast improvement over the earlier ICR instruments, problems of sensitivity, resolution and exact mass measurement remained. Earlier attempts to resolve these problems have centered around the design of the ion analyzer cell.
The development of ion analyzer cells can be traced from the drift cell disclosed in U.S. Pat. No. 3,390,265 and the trapped ion cell of U.S. Pat. No. 3,742,212. In the latter, six solid metallic plates are used as electrodes with two plates perpendicular to the magnetic field within the spectrometer and the remaining four plates parallel to that magnetic field. The perpendicular plates were charged to a given dc potential while the remaining plates were charged at an opposite potential equal in magnitude to that applied to the perpendicular plates. In the improvement of the incorporated specification, the two perpendicular plates, commonly referred to as trapping plates, were charged to a given dc potential with the remaining plates charged to a lesser potential that was not necessarily opposite in charge.
An improvement over the above cells is discussed by Comisarow in International Journal of Mass Spectrometry and Ion Physics 37(1981)251-257. This improved Comisarow cell is a cubic design of six stainless steel plates enclosing a volume of (2.54 cm).sup.3. A dc voltage is applied to the trapping plates (those perpendicular to the magnetic field) while the remaining four plates are kept at ground potential. The article states that this cell has a higher resolution by a factor of four as well as greater convenience in operation and greater reliability.
A modification of a cubic cell is described by Hunter et al. in International Journal of Mass Spectrometry and Ion Physics 50 (1983) 259-74. This cell is similar to the cubic cell in that only the trapping plates (the plates perpendicular to the magnetic field) and charged while the remaining plates are kept at ground potential. However, this cell is elongated in the direction along the magnetic field.